The present invention relates to an optical signal switching apparatus using an optical switch that is used with optical communication equipment, etc. More specifically, the present invention relates to an optical signal switching apparatus that suppresses an incorrect action of the optical switch at the time of power on and/or power off.
Following speed-up and capacity increase of information transmission in recent years, an optical fiber network using an optical fiber and various optical devices has been introduced. The range of applications of the optical fiber network extends from the public communication networks to local area networks. An optical signal switching apparatus is one of the equipment used to realize an optical fiber network. An optical signal switching apparatus does not need to convert an optical signal into an electric signal which is switched to various routes, based on the converted electrical signal, in order to perform the switching function. Therefore, the construction of the optical fiber network becomes simple. Thus, the optical signal switching apparatus aids in realizing miniaturization and economization of the network.
There has been proposed for example, an optical cross connection equipment as an optical signal switching apparatus. An optical cross connection equipment is described in the "Photonics In Switching", Technical Digest PTHA5 1997 for example.
The optical signal switching apparatus generally includes an optical switch and an optical switch control unit. The optical switch is the key device of the optical signal switching apparatus. The use of a self holding type optical switch as the optical switch offers advantages due to its low consumption of electric power. The self holding type optical switch is an optical switch that maintain the state of the switch without the use of an electric power supply by using a permanent magnet, etc.
The structure of an optical signal switching apparatus is illustrated in FIG. 1. FIG. 1 illustrates that an optical switch control unit includes an optical switch driving unit and a power supply which supplies electric power to the optical switch driving unit. The optical switch driving unit generates a optical switch driving signal to drive the optical switch when an optical switch switching signal is detected. The optical switch driving unit transmits the optical drive signal to the optical switch. In FIG. 1, the optical inputs and optical outputs that are switched by the optical switch are omitted. A related optical signal switching apparatus is disclosed in Japan patent 2654437.
However the optical switch control unit described above does not take into consideration the noise that is originated in and generated by the turning on and/or off of power by the power supply. Therefore, it is easy for incorrect operation to occur at such times. More specifically, the noise originating in and generated by the tuning on and/or off of power by the power supply can possibly change the state of the optical switch that is being held.
The incorrect operation of the optical switch can result in the of loss not only large amounts of information but also has the possibility of inducing damage and a incorrect operation of other optical devices. For example, in a case where an optical switch is used with respect to a working system and a redundant system for protecting the working system, high reliability of the optical switch is required. It is essential that even when the electric power supply to the optical switch driving unit is interrupted, the optical switch should be maintained to the previously set state.